From 2e8095b70b7a41abce7b609e788ddb1d2030367d Mon Sep 17 00:00:00 2001
From: Paul Durrant <paul.durrant@citrix.com>
Date: Tue, 4 Mar 2014 17:00:43 +0000
Subject: [PATCH] Implement checksum verification as recommended in RFC1071.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
---
 src/xenvif/checksum.c | 14 ++++++++++++++
 src/xenvif/checksum.h |  6 ++++++
 src/xenvif/receiver.c | 36 +++++-------------------------------
 3 files changed, 25 insertions(+), 31 deletions(-)

diff --git a/src/xenvif/checksum.c b/src/xenvif/checksum.c
index 3ae9d57..5f9c800 100644
--- a/src/xenvif/checksum.c
+++ b/src/xenvif/checksum.c
@@ -79,6 +79,20 @@ AccumulateChecksum(
     __AccumulateChecksum(Accumulator, MappedSystemVa, ByteCount);
 }
 
+BOOLEAN
+ChecksumVerify(
+    IN  USHORT  Calculated,
+    IN  USHORT  Embedded
+    )
+{
+    ULONG       Accumulator = ~Calculated;
+
+    // See RFC 1624, section 5
+    __AccumulateChecksum(&Accumulator, (PUCHAR)&Embedded, sizeof (USHORT));
+
+    return (Accumulator == 0xFFFF) ? TRUE : FALSE;
+}
+
 static FORCEINLINE USHORT
 __ChecksumIpVersion4PseudoHeader(
     IN  PIPV4_ADDRESS   SourceAddress,
diff --git a/src/xenvif/checksum.h b/src/xenvif/checksum.h
index 6c6c417..67ed895 100644
--- a/src/xenvif/checksum.h
+++ b/src/xenvif/checksum.h
@@ -85,4 +85,10 @@ ChecksumUdpPacket(
     IN  PXENVIF_PACKET_PAYLOAD  Payload
     );
 
+extern BOOLEAN
+ChecksumVerify(
+    IN  USHORT  Calculated,
+    IN  USHORT  Embedded
+    );
+
 #endif  // _XENVIF_CHECKSUM_H
diff --git a/src/xenvif/receiver.c b/src/xenvif/receiver.c
index f163f3f..6cd35a5 100644
--- a/src/xenvif/receiver.c
+++ b/src/xenvif/receiver.c
@@ -426,7 +426,7 @@ RingProcessChecksum(
             Calculated = ChecksumIpVersion4Header(StartVa, Info);
             Ring->OffloadStatistics.IpVersion4HeaderChecksumCalculated++;
 
-            if (Embedded == Calculated) {
+            if (ChecksumVerify(Calculated, Embedded)) {
                 Packet->Flags.IpChecksumSucceeded = 1;
                 Ring->OffloadStatistics.IpVersion4HeaderChecksumSucceeded++;
             } else {
@@ -478,16 +478,10 @@ RingProcessChecksum(
                 Calculated = ChecksumPseudoHeader(StartVa, Info);
                 Calculated = ChecksumTcpPacket(StartVa, Info, Calculated, &Payload);
 
-                // Windows seems to take RFC 2460 a bit too far and replace zero
-                // TCP checksum with 0xFFFF even though there was never a provision
-                // for in 'no checksum' option for TCP.
-                if (Embedded == 0xFFFF)
-                    Embedded = 0;
-
                 if (IpHeader->Version == 4) {
                     Ring->OffloadStatistics.IpVersion4TcpChecksumCalculated++;
 
-                    if (Embedded == Calculated) {
+                    if (ChecksumVerify(Calculated, Embedded)) {
                         Packet->Flags.TcpChecksumSucceeded = 1;
 
                         Ring->OffloadStatistics.IpVersion4TcpChecksumSucceeded++;
@@ -499,7 +493,7 @@ RingProcessChecksum(
                 } else {
                     Ring->OffloadStatistics.IpVersion6TcpChecksumCalculated++;
 
-                    if (Embedded == Calculated) {
+                    if (ChecksumVerify(Calculated, Embedded)) {
                         Packet->Flags.TcpChecksumSucceeded = 1;
 
                         Ring->OffloadStatistics.IpVersion6TcpChecksumSucceeded++;
@@ -526,11 +520,6 @@ RingProcessChecksum(
                 else
                     Ring->OffloadStatistics.IpVersion6TcpChecksumCalculated++;
 
-                // RFC 2460 should not be applicable to TCP, but Microsoft seems
-                // to think it is.
-                if (Calculated == 0)
-                    Calculated = 0xFFFF;
-
                 TcpHeader->Checksum = Calculated;
             }
 
@@ -582,13 +571,7 @@ RingProcessChecksum(
 
                         Ring->OffloadStatistics.IpVersion4UdpChecksumSucceeded++;
                     } else {
-                        // RFC 2460 should not be applicable to IPv4 but it looks
-                        // like Microsoft screwed things up in its stack so we have
-                        // to cope.
-                        if (Embedded == 0xFFFF)
-                            Embedded = 0;
-
-                        if ( Embedded == Calculated) {
+                        if (ChecksumVerify(Calculated, Embedded)) {
                             Packet->Flags.UdpChecksumSucceeded = 1;
 
                             Ring->OffloadStatistics.IpVersion4UdpChecksumSucceeded++;
@@ -601,11 +584,7 @@ RingProcessChecksum(
                 } else {
                     Ring->OffloadStatistics.IpVersion6UdpChecksumCalculated++;
 
-                    // See RFC 2460
-                    if (Embedded == 0xFFFF)
-                        Embedded = 0;
-
-                    if (Embedded == Calculated) {
+                    if (ChecksumVerify(Calculated, Embedded)) {
                         Packet->Flags.UdpChecksumSucceeded = 1;
 
                         Ring->OffloadStatistics.IpVersion6UdpChecksumSucceeded++;
@@ -632,11 +611,6 @@ RingProcessChecksum(
                 else
                     Ring->OffloadStatistics.IpVersion6UdpChecksumCalculated++;
 
-                // RFC 2460 should only be applicable to IPv6 but Microsoft seems
-                // to think it applies to the IPv4 too.
-                if (Calculated == 0)
-                    Calculated = 0xFFFF;
-
                 UdpHeader->Checksum = Calculated;
             }
 
-- 
2.39.5